84 



REPORT — 1898. 



all day and quiet day diurnal inequalities because affording opportunity 

 of also comparing the quiet day results with the corresponding Kew 

 results for declination and horizontal force given in Tables III. and IV. 

 of the 1895 B.A. Report. It seemed unnecessary here to make direct 

 comparison of the monthly inequalities, and I have contented myself with 

 extracting only the quarterly inequalities for Kew for comparison with 

 the corresponding quarterly inequalities for Greenwich, formed by com- 

 bining the months in the same way as at Kew. The differences between 

 the two sets of quarterly numbers (see Table IV.) are not large ; those of 

 horizontal force are, however, the larger (1' declination = 53 of the 

 horizontal force unit of table). 



It further seemed to be of interest to make direct comparison of 

 diurnal inequality on quiet days for single months of some year at Green- 

 wich and Kew. In Table V. this is done for the equinoctial and solstitial 

 months of March, June, September, and December of the year 1894, the 

 last for which the Greenwich results are published. The values are given 

 as derived directly from observation, no correction for non-cyclic variation 

 having been applied. Being single month results, depending each on five 

 days only, the differences in declination may be considered to be on the 

 whole small, excepting in September. In horizontal force and vertical 

 force the agreement is not so good, and especially in June for horizontal 

 force, and September and December for vertical force, remembering that 

 here 1' of declination corresponds to only 5 of the horizontal and vertical 

 force unit of the table. The discordance in some months is mainly due 

 to difference of the non-cyclic increment at the two places. The values 

 in the several months are actually as follows : — 



Non-cyclic Increment, Midnight to Midnight, 1894. 



The horizontal and vertical force values are here in c.g.s. measure x lO*. 



Thus in September in declination, and in September and December in 

 vertical force, the difference between the values at the two places is large, 

 amounting in vertical force to a considerable proportion of the whole 

 diurnal movement. If corrected in these months for the non-cyclic incre- 

 ment, as locally observed, the diurnal inequalities would be brought more 

 into accord. 



In Table VI. further Greenwich declination and horizontal force quiet 

 day results, derived from Tables I., II., and III., are compared with corre- 

 sponding Kew results, as given in Table VIII. of the B.A. Report for 1895. 

 The sums of the hourly values of diui-nal inequality in declination and 

 horizontal force, taken without regard to sign, also the diurnal range 

 (difference between the least and greatest values in diurnal inequality). 



